1. Field of the Invention
The present invention is broadly concerned with an improved, closed loop pneumatic device for the conditioning of extruded products and prevention of microorganism contamination thereof. More particularly, the invention is concerned with such a closed loop system, wherein products emerging from an extrusion cooker are conveyed by positive pressure air to a cyclone separator with air exiting the separator preferably being heated prior to return thereof for pickup of additional extrudate. In this way, contamination of the products by air borne microorganisms is prevented, and the products are heat treated and conditioned prior to drying.
2. Description of the Prior Art
Extrusion cookers have long been used for the fabrication of a variety of human and animal foods. Generally speaking, such cookers include an elongated barrel having an axially rotatable auger screw therein, and an endmost extrusion die. Most commonly, these extruders are configured for high-temperature short-time (HTS) processing of starting materials and subject such materials to increasing levels of heat, pressure, and shear during passage through the extruder barrel and die. After extrusion, it is common to convey the products to a dryer where the moisture level thereof is reduced.
An example of this type of equipment is illustrated in U.S. Pat. No. 5,054,965, which is incorporated by reference herein. The '965 patent describes use of a negative pressure conveying system wherein air is drawn into the system by means of a fan forming a part of the apparatus. However, this inevitably means that airborne, potentially contaminating microorganisms are drawn into the conveying system and contact the extrudate when it is warm and moist and therefore most susceptible to contamination.
There is accordingly a need in the art for an improved conveying apparatus which minimizes microorganisms contamination of extruded products, while at the same time serving to condition and kill microorganisms in the product before final drying thereof.